PM / devfreq: Rewrite devfreq_update_status() to fix multiple bugs

The current devfreq_update_status() has the following bugs:
- If previous frequency doesn't have a valid level, it does an out of bounds
  access into the trans_table and causes memory corruption.
- When the new frequency doesn't have a valid level, the time spent in the
  new frequency is counted towards the next valid frequency switch instead of
  being ignored.
- The time spent on the previous frequency is added to the new frequency's
  stats instead of the previous frequency's stats.

This patch fixes all of this.

Signed-off-by: Saravana Kannan <skannan@codeaurora.org>
Signed-off-by: MyungJoo Ham <myungjoo.ham@samsung.com>

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index a0b2f7e0eedb774fbfa3e8fc0e41b73f10cfefd0..2042ec3656bac3b4227d63df358d6454923a5ef5 100644 (file)
--- a/drivers/devfreq/devfreq.c
+++ b/drivers/devfreq/devfreq.c
@@ -91,26 +91,35 @@ static int devfreq_get_freq_level(struct devfreq *devfreq, unsigned long freq)
  */
 static int devfreq_update_status(struct devfreq *devfreq, unsigned long freq)
 {
-       int lev, prev_lev;
+       int lev, prev_lev, ret = 0;
        unsigned long cur_time;
 
-       lev = devfreq_get_freq_level(devfreq, freq);
-       if (lev < 0)
-               return lev;
-
        cur_time = jiffies;
-       devfreq->time_in_state[lev] +=
+
+       prev_lev = devfreq_get_freq_level(devfreq, devfreq->previous_freq);
+       if (prev_lev < 0) {
+               ret = prev_lev;
+               goto out;
+       }
+
+       devfreq->time_in_state[prev_lev] +=
                         cur_time - devfreq->last_stat_updated;
-       if (freq != devfreq->previous_freq) {
-               prev_lev = devfreq_get_freq_level(devfreq,
-                                               devfreq->previous_freq);
+
+       lev = devfreq_get_freq_level(devfreq, freq);
+       if (lev < 0) {
+               ret = lev;
+               goto out;
+       }
+
+       if (lev != prev_lev) {
                devfreq->trans_table[(prev_lev *
                                devfreq->profile->max_state) + lev]++;
                devfreq->total_trans++;
        }
-       devfreq->last_stat_updated = cur_time;
 
-       return 0;
+out:
+       devfreq->last_stat_updated = cur_time;
+       return ret;
 }
 
 /**